十二、linq关联表查询自己总结的几种方式：
1、直接join（可以不使用导航属性）
2、var user1 = from b in db.sysUsers
from c in b.SysUserRoles
where b.ID == id
select b;
（必须使用导航属性）
生成的SQL：
SELECT TOP (1)
[Extent1].[ID] AS [ID],
[Extent1].[UserName] AS [UserName],
[Extent1].[Email] AS [Email],
[Extent1].[PassWord] AS [PassWord],
[Extent1].[CreateDate] AS [CreateDate],
[Extent1].[SysDepartmentID] AS [SysDepartmentID]
FROM [dbo].[SysUser] AS [Extent1]
INNER JOIN [dbo].[SysUserRole] AS [Extent2] ON [Extent1].[ID] = [Extent2].[SysUserID]
WHERE [Extent1].[ID] = 5
可以知道，是INNER JOIN。
3、Include方式(Eager loading)
var user = from a in db.sysUsers.Include("SysUserRoles").Include("SysDepartment")
where a.ID == id
select a;
（必须使用导航属性）
生成的SQL:
SELECT
[Project1].[ID] AS [ID],
[Project1].[UserName] AS [UserName],
[Project1].[Email] AS [Email],
[Project1].[PassWord] AS [PassWord],
[Project1].[CreateDate] AS [CreateDate],
[Project1].[SysDepartmentID] AS [SysDepartmentID],
[Project1].[ID1] AS [ID1],
[Project1].[DepartmentName] AS [DepartmentName],
[Project1].[DepartmentDesc] AS [DepartmentDesc],
[Project1].[C1] AS [C1],
[Project1].[ID2] AS [ID2],
[Project1].[SysUserID] AS [SysUserID],
[Project1].[SysRoleID] AS [SysRoleID]
FROM ( SELECT
[Limit1].[ID] AS [ID],
[Limit1].[UserName] AS [UserName],
[Limit1].[Email] AS [Email],
[Limit1].[PassWord] AS [PassWord],
[Limit1].[CreateDate] AS [CreateDate],
[Limit1].[SysDepartmentID] AS [SysDepartmentID],
[Extent2].[ID] AS [ID1],
[Extent2].[DepartmentName] AS [DepartmentName],
[Extent2].[DepartmentDesc] AS [DepartmentDesc],
[Extent3].[ID] AS [ID2],
[Extent3].[SysUserID] AS [SysUserID],
[Extent3].[SysRoleID] AS [SysRoleID],
CASE WHEN ([Extent3].[ID] IS NULL) THEN CAST(NULL AS int) ELSE 1 END AS [C1]
FROM (SELECT TOP (1) [Extent1].[ID] AS [ID], [Extent1].[UserName]
AS [UserName], [Extent1].[Email] AS [Email], [Extent1].[PassWord] AS
[PassWord], [Extent1].[CreateDate] AS [CreateDate],
[Extent1].[SysDepartmentID] AS [SysDepartmentID]
FROM [dbo].[SysUser] AS [Extent1]
WHERE [Extent1].[ID] = 4 ) AS [Limit1]
LEFT OUTER JOIN [dbo].[SysDepartment] AS [Extent2] ON [Limit1].[SysDepartmentID] = [Extent2].[ID]
LEFT OUTER JOIN [dbo].[SysUserRole] AS [Extent3] ON [Limit1].[ID] = [Extent3].[SysUserID]
) AS [Project1]
ORDER BY [Project1].[ID] ASC, [Project1].[ID1] ASC, [Project1].[C1] ASC
是LEFT OUTER JOIN。
十三、辅助器
1,内联辅助器，定义在视图里没有返回值的方法，只在该页面有效。以@helper定义。
2,外部辅助器，定义mvchtmlstring对象的扩展方法，内部定义html元素用TagBuilder类。
3,内建辅助器，包括表单辅助器、普通input辅助器、强类型input辅助器、普通select辅助器、强类型select辅助器、生成链接的辅助器等。
十四、分段
1、在视图中使用@section定义分段内容，在布局中通过@RenderSection(分段名称)使用。
2、通用的部分可以定义成分段，如header、footer，甚至body也可以，布局中使用@RenderSection("header")、@RenderSection("footer")、@RenderSection("body")来使用分段；
3、IsSectionDefined(分段名称)检测分段是否已定义；
4、通过@RenderSection(分段名称,false)重载参数指定分段是否必须定义，如未定义也不会抛出异常。
十五、子动作
ChildActionOnly对于子动作不是必须的，加上是为了防止用户直接调用；
十六、模板视图辅助器（Templated View Helper）
不指定用什么HTML元素显示类型的属性，而是让MVC框架自己去判断该用什么样的HTML元素。
1、显示视图（如Display、DisplayFor）和编辑视图（如Edit、EditFor）
2、Display、DisplayFor、Edit、EditFor、Lable、LableFor、DisplayText、DisplayTextFor
3、支架（Scaffolding）
是为一个模型对象（而非针对单个属性）的所有属性生成HTML辅助器的套件。
DisplayForModel()
EditForModel()
LableForModel()
4、模板辅助器与HTML辅助器的区分（自己总结）
模板辅助器不明确指定用哪个HTML元素显示，让MVC自己去判断；
HTML辅助器包括表单辅助器、Input辅助器、select辅助器、生成url辅助器等，是明确指定了用什么HTML控件来生成；
模板辅助器更加灵活；
5、总结：
模板（视图）辅助器有两大类，一类叫做模板辅助器，其作用就是在视图中为模型的个别属性创建显示/编辑视图；
另一类叫做支架模板视图，其作用是在视图中创建模型的所有属性的显示/编辑视图。